The solution is simple, there is LG EQ and EQ button on the remote control of the home theatre, use the button to switch to NAT PLUS or BASS BOOST, those are the only two modes that support all speakers sounding at once.
Most receivers have setup menu where one can check that connections are OK. In order to hear all five speakers, you must provide surround source (eg DVD movie with surround sound), or use your home theather' options to simulate surround from stereo signal.
Do all the speakers work OK when you play a DVD?
If so check the audio settings in the TV menu. It may be set to output in PCM stereo instead bitstream surround sound.
The solution is simple, there is LG EQ and EQ button on the remote control of the home theatre, use the button to switch to NAT PLUS or BASS BOOST, those are the only two modes that support all speakers sounding at once.